A conventional thermal fixing device for an electro-photographic type image forming device includes a tubular film, a heater disposed in an internal space of the film, a pressure roller providing a nip region in conjunction with the film, and a flange located an inner side of the film for guiding rotation of the film.
In the conventional thermal fixing device, the flange is provided with a film sliding portion including a movable wall that is movable in a radial direction of the film. The movable wall includes an outer surface that has a circular arc shape. The outer surface of the movable wall is in surface contact with an inner peripheral surface of the tubular member. The movable wall is urged by a spring to provide a tensile force to the film. Hence, a slack of the film can be prevented.